There is a distinct need for carbonate polymer moldings that are resistant to ionizing radiation so that they can be sterilized without substantial loss of clarity and physical characteristics.
Stabilization of polycarbonate resins to ionizing radiation for sterilization by the addition of poly(oxyalkylene) derivatives is known. See for example U.S. Pat. No. 4,904,710, EP-A-296473, EP-A-338319, U.S. Pat. No. 4,874,802, EP-A-359366, U.S. Pat. No. 4,804,692, U.S. Pat. No. 4,873,271, and EP-A-439763. However, these carbonate polymers are not sufficiently stabilized against yellowing, especially when irradiation occurs in the absence of oxygen.
Stabilization of carbonate polymer compositions to ionizing radiation for sterilization by incorporating certain specific types of sulfur containing compounds is known. For example, incorporating a disulfide is disclosed in U.S. Pat. No. 4,939,185, incorporating a sulfoxide is disclosed in JP 08311322 A2, incorporating a sulfone is disclosed in U.S. Pat. No. 4,880,855, JP 09124918 A2 and JP 08311323 A2, incorporating a sulfonate is disclosed in JP 08311324 A2, JP 09031315 A2, JP 09310010 A2 and JP 09003314 A2, and incorporating a thiadiazole and a thiazole is disclosed in U.S. Pat. No. 4,880,856.
Further, stabilization of carbonate polymer compositions to ionization radiation for sterilization by incorporating poly(oxyalkylene) derivatives and sulfur containing compounds is known. For example, incorporation of a poly(oxyalkylene) derivative and a disulfide is disclosed in EP 572889 A1, EP 732365 A1 and EP 611797 A1, incorporation of a poly(oxyalkylene) derivative and a sulfoxide or sulfone is disclosed in JP 09176479 A2 and EP 794218 A2, incorporation of a poly(oxyalkylene) derivative and sulfonates is disclosed in EP 535464 A2, and incorporation of a poly(oxyalkylene) derivative and a sulfamide is disclosed in EP 664321 A1 and EP 742260 A1.
However, the carbonate polymer compositions thus obtained by utilizing any of such methods have drawbacks. These carbonate polymer compositions are not sufficiently stabilized against yellowing. Further, compositions containing these sulfur containing compounds show undesirable molecular weight degradation which can adversely affect the physical properties, for example, the strength of the carbonate polymer. The present invention addresses these problems.